This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application entitled BUBBLE-JET TYPE INK-JET PRINTING HEAD filed with the Korean Industrial Property Office on Sep. 30, 2000 and there duly assigned Ser. No. 2000/57627.
1. Field of the Invention
The present invention relates to an ink-jet printing head, and more particularly, to a bubble-jet type ink-jet printing head having a concavely hemispherical heater.
2. Description of the Related Art
Ink-jet printing heads are devices for printing a predetermined color image by ejecting a small volume of printing ink on a desired position on a recording sheet. The ink ejection mechanism of an ink-jet printer is largely categorized into two types: an electrothermal transducer type (or bubble-jet type) in which a heat source is employed to form a bubble in ink causing ink droplets to be ejected, and an electromechanical transducer type in which a piezoelectric bends to change the volume of ink causing ink droplets to be expelled.
According to the bubble-jet type ink ejection mechanism, if power is applied to a heater consisting of resistive heating elements, ink which is in contact with the surface of the heater is rapidly heated to a high temperature of 400xc2x0 C. forming a bubble on the surface of the heater. The produced bubble expands to impose pressure on an ink chamber filled with ink, which cause drops of ink near a nozzle to be ejected from the ink chamber through the nozzle.
An ideal ink jet printhead is 1) easy to manufacture, 2) produces high quality color images, 3) is void of crosstalk and backflow between nozzles, and 4) is capable of high speed printing. What is needed is a design for an ink jet printhead that achieves these goals.
It is therefore an object of the present invention to provide an improved ink jet printhead design.
It is also an object of the present invention to provide an improved heater design in a bubble jet ink jet printhead.
It is still an object of the present invention to provide a bubble-jet type ink jet printing head having a concavely hemispherical heater, which is capable of effectively utilizing energy supplied to the heater for bubble formation.
It is further an object to provide an ink jet printhead that can resupply ink to the ink chamber from all 360 degrees directions.
It is yet an object of the present invention to provide a heater with a flange having a high resistance to produce a bubble first about the flange portion to prevent backflow and crosstalk between nozzles.
Accordingly, to achieve the above objectives, the present invention provides a bubble-jet type ink-jet printing head including a nozzle plate in which a plurality of nozzles, through which ink is ejected, are formed, a substrate for supporting the nozzle plate, on which a plurality of heaters having three-dimensionally concave surfaces oppose the plurality of nozzles, respectively, electrodes which are formed on the top surface of the substrate and electrically coupled to each heater so as to apply current to the heater, a plurality of ink chambers which are formed between the bottom of the nozzle plate and the surfaces of the corresponding heaters and filled with ink, and an ink feed channel, formed between the nozzle plate and the substrate so as to connect with the ink chambers, for supplying ink to the ink chambers. Preferably, the heat generated per unit area is substantially uniform over the entire concave surface of each heater. This allows the bubble to be uniformly formed and developed over the entire concave surface of the heater.
Each heater is substantially hemispherical. The shape of the heater concentrates expansion energy of a bubble formed on the surface of the heater toward the nozzle, thereby improving the energy efficiency. Furthermore, each heater includes a hemispherical member and a flange disposed along the rim of the hemispherical member. This feature of the heater not only improves the energy efficiency as described above but also prevents a back flow of ink by bubbles formed on the flange. Preferably, the ink feed channel connects with the entire circumference of each ink chamber. Thus, ink can quickly refill the ink chamber after the ejection of an ink droplet, thus increasing the ejection driving frequency. Ink feed channel may be formed on the bottom surface of the nozzle plate or on the top surface of the substrate to a predetermined depth.